Elektor_Mag_-_January-February_2021

lektor January & February 2021 91

For the measurement of high value aluminum
electrolytic capacitor, it is important to choose
a test frequency that matches this technol-
ogy and is less than its resonance frequency.

Inductor (Figure 6)
For an inductor it is possible to superimpose
a DC current between 0 mA and 50 mA on
the test signal (see paragraph 3.1.5 DC bias of
the Operating instructions document). Care
must be taken to ensure that the DC voltage
developed in the internal resistance by this
bias current is less than 0.3 V, otherwise the
automatic offset circuit of the U7 differential
amplifier can no longer work properly.

NOTE: The application of 50 mA bias results
in an increase of approximately 210 mA in the
total current drawn by the device. Make sure
that your power source can supply it.

For small RF inductances, make sure the
measurement is made at sufficiently high
frequency, so that the dominant part of the
impedance is inductive!
190311-B-01

Also follow this project on the Elektor Labs project
page [2], where the author also responds to questions
and comments.

Contributors

Idea, Design, Text and Illustrations:

Jean-Jacques Aubry

Schematics: Kurt Diedrich

Editors: Luc Lemmens, Denis Meyer

Layout: Giel Dols

Comparative measurements :

Alfred Rosenkränzer

Questions or Comments?

Do you have questions or comments

about his article? Email the author

at  [email protected].

related projects

> Elektor “Kickstarter” Project:

Kit including Main Board + Display Extension Board + all parts

http://www.elektor.com/lcr

DETERMINING

COMPONENT TYPE AND

EQUIVALENT CIRCUIT

This device is designed to measure

three types of components (resistors,

capacitors, inductors) and for each of

the types the conditions of measurement

are to be chosen according to its value

and its use. In addition to the value of the

main parameter, which characterizes the

component type, it also has a secondary

parameter that depends mainly on the test

frequency. The device evaluates the nature

of the component based on its equivalent

equation:

Z = Rs + jXs

from which it calculates the quality factor:

Q = |Xs|/Rs

In AUTO mode the decision criterion for the

definition of the main parameter and the

equivalent circuit is the value of Q (=1/D)

and the sign of the reactive component Xs,

see Figure 8 for the relationship between

Q, Xs and equivalent circuit.

M

F

Ω

Figure 8. Equivalent circuit based on quality

factor and reactive component. (source:

Fluke)